A smart antenna system exploits space diversity by employing an array of antennas whose radiation pattern can be aligned in a direction of arrival (DoA) of a specific signal to be detected. As a result, a Quality of Service (QoS) can be improved, co-channel interference can be reduced, and a capacity of the system can be increased.
Smart antennas can be installed on a base station side or on a user terminal side. When smart antennas are employed at the base station, a DoA of a desired signal transmitted from a source of interest (i.e., user terminal) needs to be determined. Once the DoA is computed, then a radiation pattern (beam) of smart antennas can be oriented in the desired direction using some beam forming technique instead of utilizing uniform radiation pattern. As the user terminal moves around the cell, the smart antenna system updates the DoA and aligns the radiation beam at the base station in the direction of the user terminal. On the other hand, when smart antennas are employed at the user terminal, it is required to determine a DoA of a signal transmitted from a serving base station.
In an exemplary case when smart antennas are implemented at the base station, a sub-space analysis algorithm can be applied at the base station in order to find the DoA of a signal transmitted from a specific user terminal, such as MUltiple SIgnal Classification (MUSIC) algorithm or Estimation of Signal Parameters via Rotational Invariance Techniques (ESPRIT) algorithm. Both of these algorithms start searching from one point in space and search the entire space of interest. Computational complexity of these algorithms increases exponentially as the number of active user terminals in the system increases. Because of high computational complexity of sub-space searching algorithms, a special dedicated digital signal processor (DSP) can be required to be implemented at the base station for computing directions of arrivals of all served user terminals in the system. Moreover, these searching algorithms can have limited accuracy, especially if a large space needs to be examined.
Therefore, there is a need in the art for a method that simplifies search for a direction of arrival of a specific signal while providing sufficient accuracy.